TX 657 
.S5 G8 
Copy 1 



THE 

UNIVERSITY OF MISSOURI 

BULLETIN 



Volume 16, Number 27 



ENGINEERING EXPERIMENT STATION SERIES 16 



THE ECONOMICS OF ELECTRIC 
COOKING 

BY 

P. W. GUMABR 

Instructor in Electrical Engineering 




UNIVERSITY OP MISSOURI 

COLUMBIA, MISSOURI 

September, 1915 



Monograph 



\ 



THE 

UNIVERSITY OF MISSOURI 

BULLETIN 

Volume 16, Number 27 



ENGINEERING EXPERIMENT STATION SERIES 16 



THE ECONOMICS OF ELECTRIC 
COOKING 

BY 

P. W. GUMAER 

Instructor in Electrical Engineering 




UNIVERSITY OF MISSOURI 

COLUMBIA, MISSOURI 

September, 1915 






CONTENTS 

PAGE 

Introduction 3 

Descriptions of ovens used 3 

Description of other apparatus used 7 

Theory and purpose of cooking 9 

Losses of energy in electric ovens 13 

Meat cookery 25 

Baking experiments 42 

Economical thickness of heat insulation 52 

Summary 57 

Conclusions 58 



D. of D. 
1915 



(2> 



The Economics of Electric Cooking 

INTRODUCTION 

The present status of electric cooking might be compared in a 
way with the condition of electric lighting about 1890. Electric light- 
ing had then passed beyond the experimental stage and was used 
commercially but no exhaustive study had been made of the science of 
illumination with a view to obtain the greatest efficiency. Today, 
electric cooking has passed beyond the experimental stage and is used 
commercially, but as yet no study has been made of the variable 
conditions affecting this work, or the combination which will produce 
the greatest efficiency. 

The first electric light fixtures were obtained by wiring the gas 
fixtures then in general use. Afterwards special types of fixtures were 
developed which were more adapted to the use of electricity. Similarly, 
the first electric ovens were obtained by replacing the gas burners of 
a gas oven with electric heating coils. Some further improvement has 
been made by adding heat insulation, but as yet little attention has 
been given to the proper conditions of cooking which make for greatest 
convenience and economy in operation. With inefficient stoves and 
cheap fuels the need of such an investigation has not been apparent. 
Since in a coal range only a very small percentage of the heat energy 
in the fuel is absorbed by the food, it makes but little difference 
whether a particular article of food is cooked for half an hour at 
200°C. (392°F.) or for one hour at 150°C. (303°F.) as long as the final 
quality of the food is satisfactory. 

It was the purpose of the investigations which form the basis of 
this article to study the operation and the design of electric ovens with 
the view to determine some of the factors which will increase the 
economy and hence the popularity of electric cooking. While the actual 
results here presented are not as definite and illuminating as hoped 
for, yet it is believed they will not be without practical value as a 
contribution to what is a very complex subject. 

Particular attention is called to the fact that much of the infor- 
mation contained herein is made easily available to the understanding 
by the use of plotted curves. 

DESCRIPTION OF OVENS USED IN THE TESTS 

In order to determine the amount of energy used in electric cook- 
ing and the best methods of preparing various articles of food for 
an electric oven, tests were made on three commercial and several 

(3) 



4 UNIVERSITY OF MISSOURI BULLETIN 

experimental ovens. Each commercial oven was selected as represent- 
ing a general type of electric oven in use for domestic cooking. 




Fig. 1 

Fig. 1 shows a large range suitable for a good sized family. The 
inside dimensions of the oven are 18 inches by 12 inches by 12 inches. 
Two heating units are used, one in the top and one in the bottom of 
the oven. Each unit consists of two heating coils controlled from a 
snap switch on the front of the oven so as to consume 22<», 440, or 
880 watts continuously. From one to two inches of mineral wool is 
used as heat insulation. The outside surface of the oven is blued 
steel and it is finished with nickeled legs and trimmings. The oven 
door is 12 by 18 inches and 1.5 inches thick. It fits tightly and clamps 
securely in place when shut. Three heating units are also placed on 
top of the range for cooking not done in the oven. Fig. 2 is a cross 
section of the oven thru the center, showing the position of the heat- 
ing coils and the thermo-couple used to measure the temperature in 
these experiments. 

Fig. 3 shows a small, well-insulated oven (No. 2) suitable for a 
small or medium-sized family. The inside dimensions of the oven 
are 9.5 inches wide, 10 inches deep, and 12 inches high. The inside 
finish is seamless drawn aluminum and the outside is blued steel with 
nickeled trimmings. Two and one-half inches of mineral wool is 
used for heat insulation. An ironclad heating element is placed in the 
bottom of the oven. This heating element consumes continuously 500 
watts when connected to a 110 volt circuit. The heat cannot be turned 



THE ECONOMICS OF ELECTRIC COOKING 5 

partly off as there is only one heating element. There is no heating 
unit in the top of the oven. Underneath the oven is an automatic tem- 
perature control which may be set at various values by means of a 
dial. The dial is graduated in arbitrary numbers from l'to 11. When 




FIG. 2 CR055-SECTIOIN OVEN NO. J 
the handle of the dial is set at a given number, a thermostat will open 
the circuit of the heating element as soon as the inside of the oven has 
reached a temperature corresponding to the given number. As the 
oven cools, the thermostat must be reset by hand by pushing the handle 



6 UNIVERSITY OF MISSOURI BULLETIN 

of the dial. Fig. 4 is a cross section of the oven thru the center show- 
ing the position of the heating coil and the thermo-couple used in the 
experiments. 

Fig. 5 shows oven No. 3, one of the well-known makes of fireless 
cookers with a heating element placed underneath the inner lining. 



mm 




_ X 



Fig. 3 



The inside dimensions are 10.5 inches deep and 11.5 inches in diam- 
eter. The inside lining is seamless aluminum and the outside finish 
is varnished oak. The sides and bottom are insulated with powdered 
kieselguhr, while the cover is insulated with granulated cork. Fig. 
6 is a cross section of the oven showing the heating coil and thermo- 
couple. This oven uses 500 watts on 110 volts. There is no method of 
turning the energy partly off. 

Oven No. -4 was built by the Engineering Experiment Station. 
The inside dimensions were the same as oven No. 2. A 440, 880-watt 
heating unit was placed in the bottom of the oven and a 440-watt unit 
in the top as shown in Fig. 7. Sheet iron was used for the inside 
lining of the oven. A 4-inch layer of a commercial brand of diatoma- 



THE ECONOMICS OF ELECTRIC COOKING 7 

ceous insulating brick was used for insulation. Later four inches of 
cork board was added as shown in the drawing. This was put on 
with cement and no outside covering was used except on the front and 
the door, which were covered with wood. 




FIG. 4 CROSS-SECTION of OVEN N0.2. 

APPARATUS USED 

The energy used was measured by means of indicating watt me- 
ters calibrated by comparison with Weston laboratory standards, and 
by an induction watt-hour meter calibrated at frequent intervals by 
comparison with a rotating standard. 

The temperature of the ovens was measured by means of copper- 
constantan thermo-couples with which an accuracy of 0.1 degree is 
obtainable when used below 360°C. 1 (680°F.). A Siemens-Halske indi- 



1. Adams and Johnson. Am. Jour, of Science, June, 1912. 



8 



UNIVERSITY OF MISSOURI BULLETIN 



eating galvanometer and a Bristol recording galvanometer were used 
to determine the e.m.f. of the thermo-couples. The recording gal- 
vanometer traced a curve by intermittent contact on a circular smoked 
chart. Both the indicating and the recording galvanometer were cali- 
brated for the copper-constantan thermo-couples by means of mercury 
thermometers which had been certified by the Bureau of Standards. 
The thermo-couple and the thermometer were immersed in an oil bath 
which was slowly heated and carefully stirred. Simultaneous readings 
were taken of the galvanometer and the thermometer. Fig. 8 shows a 




Fig. 5 



diagram of the connections used for the galvanometers and thermo- 
couples. 

In the oven the wires of the thermo-couple were enclosed in a 
glass tube and separated by mica. Outside the oven they were en- 
closed in rubber tubing. The cold junction was kept at 0°C. (32°F.) 
by immersion in ice water. 

In oven No. 1 an extra thermo-couple was inserted for measuring 
the internal temperature of the food. The wires entered the oven thru 
two glass bushings and were left bare except for a 3-inch glass tube 
at the end which was inserted in the food. The wires were long 



THE ECONOMICS OF ELECTRIC COOKING 



9 



enough so that after the food was cooked it could be placed on a shelf 
just outside the oven to cool without removing the thermo-couple from 
the food. In order that the wires would not short circuit either on 
themselves or on the lining of the oven all the slack was pulled out- 
side the oven. 



COVER 




FIG. 6 CROSS-SECTION o> OVEM MO 3 



THEORY AND PURPOSE OF COOKING 

In order to understand some of the problems which must be 
worked out before an ideal electric cooking device can be perfected, 
a word about the purpose of cooking food will not be out of place. 
The objects of cooking food are, briefly: (1) to render it more digest- 
ible so that the nutrient parts can be easily absorbed by the digestive 
organs; (2) to render it more appetizing by improving its appearance 
and developing in it new flavors; (3) to sterilize it to some extent thus 
delaying incinient putrefaction. The relative importance of these 

2 



10 



UNIVERSITY OF MISSOURI BULLETIN 



objects depends upon the article of food which is to be cooked. For 
instance, in cooking animal foods the most important objects to be 
attained are to improve the flavor and appearance and to sterilize 
them. In fact, the cooking of animal foods such as meat, eggs, and 
fish which are rich in proteids actually decreases their digestibility. 
This is true at least of the chemical processes of digestion. The in- 



CORK BOARD 




FIG. 7 CR0S5-SECT)0H OVEri no. 4 



creased attractiveness, however, of well-cooked food may render it 
indirectly more digestible by causing a greater flow of the digestive 
juices. 

The effects of applying heat to various foods can be more easily 
understood by first considering the effect of heat on the various chemi- 



THE ECONOMICS OF ELECTRIC COOKING 



11 



cal constituents of which protein, starch and fat are the most impor- 
tant. The effect of heat on the protein of foods is to coagulate it. 
This change occurs at the comparatively low temperature of 75 °C. 
(167°P.). If the temperature is increased much above this point the 
protein tends to shrink and harden, and the digestibility of the food 
of which it is a part is proportionately lessened. This fact can be 
easily demonstrated in the case of the white of an egg. If an egg 
cooked for ten minutes in water at a temperature of 75 °C. is com- 
pared with one cooked in the ordinary way, that is, for three minutes 
in boiling water, it will be found that the albumin of both are solid 
thruout, but in the case of the former it will consist of a tender jelly, 
whereas in the boiled egg it will be dense and almost leathery. 



Constantan Wire. 




Recording Indicating 

Galvanometer. Galvanometei 



Cold Junctions 



Hot Junctions 



F"IG 8. Connections or thermo-couple* and galvanometcrs 

The investigations of Meyer, 1 Harcourt, 2 and Day 3 demonstrate 
that starch consists of microscopic grains or cells which are but 
slightly soluble in cold water. These grains are composed of layers. 
The inner and outer layers have distinct properties. The inner layers, 
called blue amylose because of the color which they give with iodine, 
are very slowly digested in the raw state. They take up water at from 
60° to 80 °C. (140° to 176 °F.) and form a sticky collodial substance 
known as starch paste, in which form the inner portion is very easily 
digested. Long boiling to the extent of three hours does not make it 
more digestible. The outer layers of the starch (called red amylose) 
give a red color with iodine, and are more difficult of digestion or 
change in water than the inner portion of the starch grain. When 
starch paste is made without boiling, the outer layer stretches tho it 



1. Untersuchungen iiber die Starkehorner, Jena, 1895, p. 107. 

2. Ann. Rpt. Ontario Ag. Col. and Exp. Farm 32, p. 63. 

3. U. S. Dept. of Agr. Bui. 302. 



12 UNIVERSITY OF MISSOURI BULLETIN 

does not break. In this condition it is easily permeable and does not 
interfere with the more rapid digestion of the inner portion. When 
starch paste is boiled Doctor Day found that a more homogenous tho 
not more digestible paste results. Dry heat at 150°C. (302°P.) or 
higher converts starch into a soluble form, and finally into dextrin. 
This change occurs to a limited degree in the crust of bread and in 
the making of toast. 

In many vegetables and unground cereals the starch grains are 
enclosed in woody, fibrous, or cellulose walls which are but slightly 
affected by the digestive juices. The effect of cooking by the applica- 
tion of moist heat causes the starch grains to swell and to finally 
rupture the cellulose walls. This process occurs at temperatures much 
below the boiling point of water as shown by the values x given in 
Table I. 

Table I. 

Oats 85 : Cent. ( 1S5 : F. i 

Barley SO '- Cent. ( 176 D F. i 

Wheat SO : Cent. 1 176 F. I 

Rice 80° Cent. ( 176 " F. » 

Maize 75 c Cent. (167°F.) 

Potato 65 : Cent. 1 140 F. I 

Since the fats of food are apparently but slightly affected by cook- 
ing,- their consideration is not of as much importance as protein or 
starch. The only change that has been detected in the composition of 
fats in cooking is a tendency to form free fatty acids at high tempera- 
tures (250 C C.) (4S2-F.) which are thought to .be irritating to the 
stomach. 

The ideal preparation of food for human use requires that the nu- 
trient which it contains shall be utilized to the fullest extent. X I 
only should the food be in such a state that the digestive juices can best 
act on it, but these digestive juices should be properly stimulated to 
do their work, by improving the taste or flavor of the food. 

The present day problem is to determine the methods of cooking 
which will yield the most in nutrition and flavor with a minimum 
expenditure of fuel and labor. The solution of this problem will re- 
quire careful research by the physiological-chemist, the domestic 
scientist and the manufacturer of cooking apparatus. Taking into 
consideration the results of experiments on the digestibility of foods 
cooked in various ways, the problem of the domestic science de- 
partment is to definitely determine the range of temperatures and the 



1. Svkes. Principles of Brewing, p. 

2. V. S. Dept of Agr. Farm Bui. No. 526. p. 14 



THE ECONOMICS OF ELECTRIC COOKING 13 

time of cooking at each temperature for all classes of food. Effects of 
quality and proportion of ingredients, size of utensils, and other varia- 
bles must be studied so that definite rules and tables can be worked 
out giving the most desirable times and temperatures of cooking any 
article of food. 

The problem of the electrical engineer is to determine from the 
range of temperatures for cooking any given article of food, the particu- 
lar temperature which is the most economical. He must also perfect 
an electric cooking apparatus which will maintain the desired tem- 
perature with a minimum amount of attention, and which will be low 
in first cost and economical in operation. 

LOSSES OF ENERGY IN ELECTRIC OVENS 

During the last century there has been a great advancement in 
the methods of applying heat to food. Each improvement has resulted 
in less of the heat energy being wasted and in more being absorbed 
by the food. Each step, from the open fireplace to the coal range, 
to the gas stove, and finally to the electric oven has been marked by 
the use of more expensive fuel, greater heat efficiency, and better con- 
trol of the heat. 

Except in a few localities, for the same number of heat units de- 
livered at the meter, electricity is more expensive than gas or coal. 
Hence, it is only by studying carefully the most economical features 
of design and operation of electric cooking apparatus that electricity 
will be able to compete with gas and coal. A study of the heat losses 
in cooking is, therefore, of considerable importance to the designer of 
electric cooking apparatus. 

Convection and Radiation Losses. If an electric oven is supplied 
with electric energy at a constant rate, say 1000 watts, the temperature 
of the oven will at first increase rapidly and then more slowly until 
it finally reaches a constant value. From the law of the conservation of 
energy it follows that if there is no food in the oven, the same amount 
of energy is lost into the room that is supplied by the heating coil. 
This heat is lost in two ways, — by radiation and by convection. 

The radiation loss consists of waves of energy similar to light 
waves but of different length. The amount of the energy radiated de- 
pends upon the nature of the surface, its temperature, and the tem- 
perature of the room. It is independent of the shape of the radiating 
surface. The convection loss, however, depends upon the shape and 
the position of the surface as well as the temperature of the surface 
and the surroundings. It is independent of the nature of the surface. 

The radiation and convection losses from horizontal and vertical 
plane surfaces have been determined by Langmuir x for various ma- 



1. Trans, of Am. Electro-Chem. Soc, Vol. 22, p. 299 (1913). 



14 



UNIVERSITY OF MISSOURI BULLETIN 



terials. Fig. 9 shows the convection and radiation losses for vertical 
plane surfaces for temperatures up to 250 °C. (482°F.), the highest 
temperature used in cooking. Fig. 10 shows the convection losses for 
vertical and horizontal surfaces as given by Langmuir. 

As shown by the curves the radiation loss from a black body con- 
stitutes a large part of the total loss, while the radiation from a pol- 
ished silver surface forms but a small part of the total loss. For all 
other surfaces the radiation loss lies between that of a silver surface 
and a black surface; the convection loss being the same for all sur- 
faces. 



i 




T 









(0 






FIG. 3 
ES SHOWING TOTAL- LOSSES 












CURV 


> 








DC 




FROM HEATED SURFACES IN AIR. 








Q. 




CONVECTION LOSS IS FOR 


/ 


/ 








VERT ,r * AI *' ,D,rArF 


-i/ 




V 
















r 


/ 




% 
















/, 

f/ 


^ 





























5 




















„e^ 






£o.2 

+ 










> 


// 


r 


^ L^ 




z 



Po.i 

8 








S 


^ 


' 




s=ggs 


















*%0^ 








> 
z 



























SO IOO ISO ZOO 250 




TE 


MPER/ 


VTURt 


IN 




DE6R 


E.E* 


< 


MENTIS 


RADE 





There are two ways in which the heat losses of an electric oven 
may be reduced. Consider an oven of given inside dimensions built 
on the plan of the ordinary gas oven, with a black outside surface and 
no heat insulation. The temperature of the outside surface will be 
within a few degrees of the temperature of the oven. A large amount 
of energy will be required to maintain a cooking temperature inside 
the oven. Since the convection and radiation losses depend on the 
temperature of the outside surface, the losses will be greatly reduced 
if this temperature can be decreased. If the inner and outer surfaces 
of the oven are separated a few inches and the intervening space filled 
with some poor conductor of heat such as mineral wool, kieselguhr. or 
diatomaceous earth, there will be a large drop in temperature between 



THE ECONOMICS OF ELECTRIC COOKING 



15 



the inner and outer surfaces, because the heat will be conducted away- 
very slowly from the hot interior. 

Suppose that enough heat insulation were introduced to reduce the 
outside temperature from 200°C. (392°F.) to 110°C. (230°F.), the 
watts lost per square centimeter of outside surface would be reduced 
from 0.37 to 0.12 as shown by the curves of Fig. 9. Stated in another 
way, the energy required to maintain the inside temperature of the 
oven at its former value would be reduced from 1000 watts to 325 watts 
for the same amount of outside surface. For the same inside dimen- 
sions, however, the area of the outside will be greater because of the 



6 
tnzo 

6 

0. 

•) 

h 

1 



1.0 





























FIG. IO 

CURVE SHOWING CONVECTION 

FROM PLANE SURFACES 


























yy 


















& 


& 


















2^ 




202* 










O 




^£52^ 











50 IOO ISO 200 

TEMPERATURE OF SURFACE IN PEGREES CENTIGRADE 



2SO 



added insulation, hence the reduction in energy will not be quite in 
the proportion indicated. 

Another method of reducing the heat losses would be to silver 
plate the outside surface of the oven. The heat loss would then be 
decreased from 0.37 watts per sq. cm. to 0.13, or the energy required to 
maintain the same inside oven temperature would be reduced from 
1000 watts to 350 watts. By a combination of the two methods the 
input of the oven for the required internal temperature would be re- 
duced from 1000 watts to 165 watts. 

To silverplate the outside surface of an electric oven would be 
too expensive to be practical, but there are cheaper surfaces which 
radiate a very small amount of energy compared to the ordinary black 
oven. A white enameled surface, for instance, would be much more 



16 UNIVERSITY OF MISSOURI BULLETIN 

efficient than the black surface. A place in which nickel plating could 
be used to good advantage would be around the edge of the oven 
door. Because of the good heat conductivity of the metal which con- 
nects the inner and outer surfaces of the oven around the door, the 
outside temperature of the oven is considerably higher around the 
edges of the door than elsewhere on the outside. If the nickel plating 
now used on the legs and corners of the stoves were put around the 
edge of the door, it would help to decrease the losses and the cost of 
the oven would be no greater. 

The heat losses from an electric oven can be easily determined 
by measuring the energy input and the temperature in the oven after 
equilibrium conditions are established. The heat losses for the ovens 
tested were obtained in the following manner: A thermo-couple in- 
side the oven was connected to a recording galvanometer. A given 
amount of energy was turned on so that the temperature of the oven 
increased until finally the heat lost equaled the energy measured by 
the wattmeter. The tests were continued until the oven temperature 
had remained constant for at least two hours. This was repeated for 
other values of energy input and curves were plotted between oven 
temperature and watts input as shown in Fig. 11. It will be noticed 
that the curves obtained are straight lines, all cutting the tempera- 
ture axis at room temperature. Altho very exact measurements might 
show a slight upward tendency at higher temperatures, the present 
results with a maximum error of two per cent are sufficient for prac- 
tical use. 

Since the character of the surface and the outside area will remain 
constant for a particular oven, the above curves showing the relation 
between the oven temperature and the energy lost by radiation and 
convection should be similar to the curves given by Langmuir (Fig. 9). 
The apparent discrepancy can be accounted for in that the greatest 
outside temperature of the ovens tested was only SO C C. (176 C F.) and 
below that temperature Langmuir's curves do not depart perceptibly 
from a straight line. 

As will be shown later, the temperature energy curves of Fig. 11 
are very useful in comparing the economy of various ovens for the 
cooking of any given article of food. Since one point of the curve 
will be zero energy at room temperature, only one determination is 
necessary to plot the curve for any particular oven. For a given room 
temperature measure the watts input and the temperature of the oven 
after it has become constant and plot this point on the diagram. Con- 
nect this point and a point on the temperature axis at room tem- 
perature with a straight line, and the heat lost from the oven at any 
given oven temperature may be directly taken from the diagram. 
These results indicate the energy lost thru the insulation and the 
metal around the edge of the door. To separate these items the energy 



THE ECONOMICS OF ELECTRIC COOKING 



17 



conducted thru the insulation can be directly calculated and subtracted 
from the total lost energy. 

Preheating Losses. The heat losses of an electric oven may be 
resolved into those occurring before and those occurring after the food 
has been inserted in the oven. In many kinds of cooking, such as bak- 
ing biscuits and cake, the food must be placed in a hot oven as soon as 
it is prepared. Since for domestic purposes an oven is never used con- 



700 



GOO 



500 
£400 



300 



Fie. 1 1 

CURVES SHOWING ENERGY 
REQUIRED TO MAINTAIN 
OVENS AT CONSTANT 
TEMPERATURE. 




50 IOO 150 

OVEN TEMPERATURE. IN 



2Q0 250 

DECREES CENT. 



tinuously, it cools off in the interval during which it is idle. Before 
it can be again used the inside of the oven and the contained air must 
be heated up to a cooking temperature. This operation is called pre- 
heating. The amount of energy required to preheat an oven to the 
desired temperature depends upon the insulation of the oven, the di- 
mensions, the thermal capacity of the inside, and the size of the heating 
coils. The amount of energy required to preheat the ovens tested was 
3 



18 



UNIVERSITY OF MISSOURI BULLETIN 



obtained by taking simultaneous readings of the thermometer and the 
watt-hour meter. Fig. 12 shows the results obtained. It will be noticed 
that altho oven No. 4 was better insulated than Oven No. 2 it required 
more energy for the preheating. This was probably due to the greater 
heat capacity of the inside lining and the throat. The effect of too 
small a heating coil is shown by the curve for oven No. 3. For high 
temperatures the energy required for preheating this oven is alto- 



1100 




50 IOO 150 200 

temperature: in degrees 



gether too large for the size of the oven. The fact that the heating 
coil is below the bottom of the oven also caused the oven to heat more 
slowly, the time required for it to reach the higher cooking tempera- 
tures being 2.5 hours for 250°C. (482- F.). In order that the energy 
required for preheating may be as small as possible the inner parts 
of the oven should have the least practical heat capacity and the heat- 
ing coils should be large enough to bring the oven to the desired tern- 



THE ECONOMICS OF ELECTRIC COOKING 



19 



perature in a fairly short time. If the time required for the oven to 
reach the cooking temperature is excessive, not only is there a delay 
in the cooking operation but a larger amount of the energy is lost into 
the room by radiation and convection during the time of preheating. 

Heat Loss When Oven Door Is Opened. In preparing food which 
cannot be placed in a cold oven and gradually heated, there is a loss of 
heat when the oven door is opened. The amount of this loss and the 




fall of temperature in the oven were determined for oven No. 1 as fol- 
lows: The energy input was measured by means of a wattmeter and 
was kept constant for each test. The temperature of the oven was ob- 
tained by means of the thermo-couple and recording galvanometer. The 
variation of the temperature of the oven when the door was opened 
for 15 seconds at three-minute intervals is shown in Fig. 13. The 
average temperature gradually changes and finally reaches a constant 



20 



UNIVERSITY OF MISSOURI BULLETIN 



value. A curve plotted for these average temperatures and the energy 
input is shown in Fig. 14. The difference between the ordinates of 
this curve and the similar curve obtained with the door closed evi- 
dently represents the energy lost by opening the door. From these 
values the energy lost each time the door is opened is readily cal- 
culated. Fig. 15 shows the watt-hours lost each time the door of oven 



IOOO 

900 

800 

^700 

a 

z 

600 

1/) 

!c 

|soo 


FIG. 14- . 
CURVES SHOWING ENERGY / 




"REQUIRED TO MAINTAIN 
CONSTANT AVERAGE. 
TEMPERATURE OF OVEN 
NO. I.DOOR OPENED IS 
SEC 3 Nl IN. INTERVALS. A 


to/ 
wf 




**/ 






















d 


.0/ 








i 


f 








/ , 


f 






300 
200 
100 






7 / 
































~A 













SO IOO ISO 200 250 

OVEN TEMPERATURE IN DEGREES CENT. 



No. 1 is opened for 15 seconds. Fig. 16 shows the fall in temperature 
of the oven when the door is opened at different oven temperatures. 

Efficiency. Of the energy input of an electric oven only the part 
which is absorbed by the food is used to advantage. The remainder 
goes to supply losses, such as radiation, convection, preheating, open- 
ing the oven door, and heating the utensil containing the food. 

The ratio of the energy utilized in a piece of apparatus in doing 
useful work to the total energy input is said to be the efficiency of 



THE ECONOMICS OF ELECTRIC COOKING 



21 



that apparatus. Using this meaning, the efficiency of cooking appara- 
tus is the ratio of the energy absorbed by the food to the total energy 
input of the fuel whether in the form of coal, gas, or electricity. 

To get a useful expression for the efficiency of a cooking device 
is not as simple a problem as it may seem. Some investigators have 
adopted the method used to determine the efficiency of a steam boiler 
and firebox. They have heated a quantity of water, calculated the 



18 



iz 



10 





FIG. 15 
ENERGY LOST WHEN 






DOOR OF OVEN NO. 1 
IS OPENED 15 SEC. 

















































































































SO IOO )50 200 250 

OVEN TEMPERATURE IN DEGREES CENT 

number of heat units absorbed by the water, and taken as the efficiency 
of the stove or oven the ratio of the heat units absorbed by the water 
to the heat units supplied by the fuel. This does not take into account 
the fundamental difference in the purpose of the cooking apparatus 
and the steam boiler. The purpose of the steam boiler is to convey 
as many heat units from the fuel to the steam as may be possible. 
That is, likewise, the purpose in heating water for domestic uses, but 
it is not the object in view when cooking food. 



22 



UNIVERSITY OF MISSOURI BULLETIN 



As explained in a previous paragraph the object in cooking food is 
to improve its flavor or to increase its digestibility or both. These 
two factors are the criteria of a well-cooked food. Very often food 
which has absorbed the greatest number of heat units is the most badly 
cooked, and the method of cooking which utilizes the largest part of 
the energy input may give the poorest results. 

As an example of why the steam boiler method of determining 
the efficiency of a cooking device is inadequate, let us suppose that a 



Id 

Q 
< 

10 SO 

£ 

z 

Id 
O 

25 
(0 
Id 
Id 
IK 

S20 




15 

















ne. 16 
curve showing fall in 
temperature: of oven 
no.i after door is 
opened for 15 sec. 


















/ 








/ 






















/a 

/ 










0/ 










/ 













50 

INITIAL. 



tOO I50 200 

TEMPERATURE. OF 



250 
OVEJM 



cereal is to be cooked for two hours at 90 C C. (,194 C F.). Only such an 
amount of water is added as will be absorbed by the cereal during 
the cooking. It is placed in a well-insulated oven, heated rapidly 
from 20° to 90°C, (68° to 194°F.), and then kept at that temperature 
for two hours by supplying just enough energy to make up for radia- 
tion losses. During the first part of the process energy will be ab- 
sorbed by the food as it is heated from the room temperature to the 



THE ECONOMICS OF ELECTRIC COOKING 23 

cooking temperature. The efficiency will lie somewhere between 20 
per cent and 70 per cent depending on the characteristics of the oven, 
its initial temperature and the size and shape of the vessel used. 
During the last part of the cooking process very little energy will be 
used by the heating coil but practically no energy will be absorbed by 
the food, so that the efficiency will be zero. 

Another oven requiring less energy for preheating and not being 
so well insulated would show a better efficiency during the first fifteen 
minutes when the food is being heated up, but during the last two 
hours would require more energy than the first oven to make up for 
the greater radiation losses. The total energy supplied might be 
greater for the second oven and yet the efficiency as calculated from 
the heating up part of the cooking process, or as determined by heat- 
ing a known quantity of water, would be less. 

Evidently, the final consideration in comparing the efficiency of 
two ovens is this, — which one will cook a given article of food in the 
best manner with the expenditure of the least amount of fuel? This 
suggests another method of specifying the operating efficiencies of 
cooking apparatus: to determine the amount of energy required to 
cook a standard article of food under standard conditions, specifying 
the quality of the food, the quantity, and the time and temperature 
of cooking. This method might prove satisfactory if the standard con- 
ditions could be determined so as to be reliable and be typical of 
average cooking processes. There would be a difficulty, however, in 
assuming any one article of food as a standard. The conditions of 
cooking vary to such an extent that a particular oven might be more 
economical for cooking one kind of food and less so for another kind. 
For instance, biscuits require a short time of cooking at a high tem- 
perature, ten to fifteen minutes at 200= to 220 C C. (392- to 428 = F.) 
while cereals and vegetables are best cooked for several hours at a 
temperature somewhat below boiling. 

Another method of indicating the efficiency of electric ovens would 
be to specify the energy required to supply the losses. The loss due 
to opening the oven door will be practically the same for all ovens 
of the same size so that the principal losses will be those due to 
radiation, convection and preheating. Evidently, when a particular 
article of food is cooked under the same conditions of time and tem- 
perature in various ovens, the part of the energy input absorbed by the 
food will be practically the same while the part of the energy input 
not absorbed by the food, or the losses, will depend upon the character- 
istics of the oven. If the energy required to heat various ovens to 
any given temperature and the energy required to maintain the oven 
temperatures at the desired value are known, then the cost of opera- 
tion of any of the ovens can easily be determined for any kind of 
cooking; providing, of course, that the time and temperature used for 
that cooking are known. 



24 UNIVERSITY OF MISSOURI BULLETIN 

For the purpose of comparison with the results of other investi- 
gators the apparent efficiency of three electric ovens and a gas oven 
were determined by heating a known quantity of water. Four thousand 
grams of water were used in each test. The water was placed in an 
aluminum dish weighing 451 grams. This dish was chosen as it was 
the one used in some meat tests to be described later. The dish was 
used without a cover. The water was weighed carefully before and 
after each test. The temperature of the water was read just before 
it was placed in the oven and just after it was removed. The energy 
used in evaporation and the energy absorbed by the dish were included 
in the total energy absorbed. One set of tests was made by placing 
the water in the oven when the temperature of the oven was the same 
as that of the room and then turning the heating units on full. Another 
set of tests was made by placing the water in the oven when the tem- 
perature of the oven was 150 °C. (302°F.) turning the heat on full 
until the temperature had returned to that value and then keeping 
the oven temperature constant for the remainder of the test. Tests 
were also made with the heating units on top of oven No. 1 and the 
top burners of the gas stove. The results of the tests are given in 
Table II. 

The high efficiency of the top heating coils is due to the good heat 
connection between the heating units and the dish of water. On top 
of the stove there is approximately one-tenth of an inch space between 
the red hot coils and the bottom of the dish while in the oven the 
coils and the dish are separated several inches with a baffle between. 
Because of the poor heat connection between the coils of the oven and 
the dish the heat is conducted very slowly from the coils to the water. 

The results of the tests indicate that water could not be heated 
as efficiently by placing it in the oven as by heating it on top of the 
stove. It does not follow, however, that all cooking can be done more 
economically on top of the stove than in the oven. The contrary may 
be true in many cases; for instance, it would be cheaper to prepare 
a pot-roast in oven No. 2 or No. 4 than it would be to prepare it on top 
of the stove on the heating coil tested. This is because the purpose of 
cooking the pot-roast is not to put the greatest amount of heat into it 
with the minimum cost, but the purpose is to keep the roast at a 
temperature of 80°C. (176°F.) for three or four hours until it is satis- 
factorily cooked. Articles of food like vegetables or a pot-roast which 
are prepared in water could be cooked still more economically by re- 
moving the baffle from the oven and placing the dish directly on the 
heating element. Advantage is then obtained of the good heat eon- 
tact between the heating coil and the dish of food and the smaller radia- 
tion losses of the oven. The best results for this kind of cooking in 
which there is enough water to prevent scorching would be obtained in 
an insulated oven but little larger than the dish containing the food. 



THE ECONOMICS OF ELECTRIC COOKING 



25 



Table II. 

Temperature of ovens at beginning of test 25° C. (77° F.). 



Apparatus 


Calories 
absorbed 


Energy 
used 


Calories 
input 


Efficiency 
percent 


No. 1. oven 


60.4 

138.9 
205.5 
106.6 


571 watt-hr. 

452 watt-hr. 

525 watt-hr. 

lieu. ft. 


492 

389 

452 

1940 


12 3 


No. 2 oven 

No. 4 oven 


35.7 
45.5 


Gas oven 


5.5 



Temperature of ovens thruout test 150° C. (3Q2° F.), 



No. 1 oven 


71.4 
109.0 
108.5 
119.0 
191.0 
243.0 


316 watt-hr. 
281 watt-hr. 
198 watt-hr. 
6.2cu. ft. 
2.75 cu. ft. 
457 watt-hr. 


272 
242 
170 
1100 
485 
393 


26.0 


No. 2 oven 


45.0 


No. 4 oven 

Gas oven 


64.0 
10.8 


Gas burner 

Top burner No. 1 oven .. . 


39.4 
61.8 



MEAT COOKERY 

Meat may be cooked by any of the methods in common 
use, — roasting, baking, frying, broiling, stewing, or boiling. Lit- 
tle has been known concerning the scientific principles of cooking 
meat until recently. Since there has been no uniformity in the prac- 
tices and processes of cooking, the terms used vary widely in their 
meaning. Roasting, — which was formerly applied to cooking over red 
hot coals, — is now used synonymously with baking or cooking in an 
oven by means of a dry heat. Stewing and boiling have never been 
clearly defined. Both apply to the cooking of meat when immersed in 
water. The present tendency in scientific literature is to use the 
term boiling when meat is cooked in water at any temperature and to 
specify the exact temperature used. Broiling and frying will not be 
discussed in this paper, since it is impractical to utilize the advantages 
of an insulated electric oven for preparing meat by either method. 

There is a wide diversity of taste in regard to the proper degree 
of cooking of a meat roast. Some people prefer that the meat should 
be heated only enough to slightly change the color of the interior, 
while others prefer the meat cooked until every trace of the pink color 
has disappeared. This difference of taste causes a corresponding varia- 
tion in the meaning of the terms used to describe the degree to which 
meat shall be cooked. The meat which one would call rare is, to 
another, medium rare, and, at times, meat that is actually raw is served 
as rare. 



26 UNIVERSITY OF MISSOURI BULLETIN 

In this paper the terms rare, medium rare, and well-done are used 
to indicate the same degree of cooking as denned by Miss E. C. 
Sprague. 1 The definitions are as follows: 

"Rare or Under-done Meat. In the center of a rare roast the dull 
bluish-red characteristic of the raw meat has changed into the bright 
rose-red of the rare meat. This shades into a lighter pink toward the 
outer portions and changes into a dark gray in the layer immediately 
underlying the outer browned crust. The ideal standard for rare meat 
requires that the larger portion of the roast shall have been heated 
only enough to effect this first change to rose-red, so that the outer 
brown crust and the intermediate gray layer shall be as thin as 
possible. Under these conditions there will be a liberal amount of 
bright red juice. 

"Well-done Meat. If the cooking is continued for a sufficient 
length of time, instead of being distended the meat shrinks noticeably. 
The whole interior is found to have become brownish-gray in color and 
the juice is scanty and either colorless or slightly yellow. Meat cooked 
to this degree is said to be well-done. 

"Medium Rare Meat. A condition between these two extremes is 
indicated by the term medium rare. In this case sufficient heat has 
been applied to change the color of the center to a light pink. The 
gray layer underlying the crust has, therefore, extended considerably 
toward the center. The free juice is smaller in quantity and lighter 
in color than in the rare meat." 

The experiments of Grindley and Sprague have demonstrated that 
beef can be satisfactorily roasted at an oven temperature anywhere 
between 100° and 200°C. (212° and 392°F.). A beef roast prepared 
at any temperature within this interval was found to be well browned 
and attractive looking. No difference was discernible in the tender- 
ness of duplicate roasts cooked at the extremes of temperature. In 
their opinion the flavor and juiciness of the meat was slightly better 
at the lower temperatures, whereas at the higher temperature the 
drippings were better flavored and larger in quantity. 

Since a roast of beef can be properly prepared at any tempera- 
ture between 100° and 200°C. (212° and 392 C F.) the most satisfactory 
temperature within this interval can be determined only by the con- 
sideration of other factors, of which the time of cooking and the cost 
of cooking are the most important. In order to determine this most 
economical temperature for roasting a rolled rib roast, a series of ex- 
periments were performed. 

Twenty-two roasts consisting of the third and fourth standing rib 
cuts, as near alike in size and quality as possible, were obtained from 
a local market. The meat was freed from bone, tightly rolled, and 



1. University Studies, Univ. of 111., Vol. 2, No. 4. p. 4. 



THE ECONOMICS OF ELECTRIC COOKING 27 

secured with wooden skewers. Samples were roasted at 100°, 120,° 
140°, 160°, and 180°C. (212°, 248°, 284°, 320° and 356°F.) The time 
required for the cooking and the amount of energy used at each tem- 
perature was measured, from which the most economical temperature 
for cooking a rolled roast was determined. 

In order to get uniform results in the degree of cooking of the 
meat it was necessary to decide on a rather exact method of deter- 
mining when the meat was sufficiently cooked. As mentioned before, 
the aim in cooking meat is not to increase its digestibility but to 
improve its flavor and appearance. This is accomplished by decompos- 
ing the red coloring matter called oxyhaemoglobin, which removes the 
raw appearance of the meat. The inside of the roast should be heated 
sufficiently to accomplish this without overcoagulating the proteids or 
removing from the meat those substances which tend to become soluble 
or volatile upon the application of heat. 

Milroy's experiments x show that approximately 50 per cent of the 
protein of fresh beef was coagulated at 50 °C. (122°F.), 70 per cent at 
60°C. (140°F.), 90 per cent at 70°C. (158°F.) and 100 per cent at 
80°C. (176°F.). At about 75°C. (167°F.) the oxyhaemoglobin under- 
goes a decomposition which probably marks the disappearance of the 
last trace of red in the meat.. These results would indicate that the 
inside of the meat ought to reach a temperature between 50° and 80 °C. 
(122° and 176 °F.) to be properly cooked, the exact temperature de- 
pending upon the degree of cooking which people prefer. 

Grindley and Sprague 2 found that if the inner temperature of a 
roast is between 55° and 65 °C. (131° and 149 °F.) the meat will be 
rare, if it is between 65° and 70 °C. (149° and 158 °F.) it will be 
medium rare, and if between 70° and 80 °C. (158° and 176 °F.) it will be 
well done. In order to secure as much uniformity as possible in the 
results, a definite temperature rather than a range of temperature was 
taken as an indication when the meat was sufficiently cooked. Fifty- 
five degrees C. (131°F.) was used for rare, 65°C. (149°F.) for me- 
dium rare, and 75°C. (167°F.) for well done which conforms to the 
usage of other experimenters. It was not always possible, however, 
to obtain the exact inner temperature to a degree, because if the 
roast is taken out of the oven when the inner portion of the meat is 
at some particular temperature, this temperature will first increase 
several degrees before it begins to decrease. This increase of tem- 
perature after the roast is removed from the oven depends upon the 
temperature of the oven in which the meat is cooked, being greater 
for a high oven temperature. The following temperatures of the roasts 
when removed from the oven were found to give the desired results: 



1. Archiv. f. Hyg., 1895, XXV., p. 154. 

2. Univ. of 111. Bui., Vol. II, p. 290. 



28 



UNIVERSITY OF MISSOURI BULLETIN 
Table III. 



Oven Temperature. 
Degrees 



Inner temperature of the meat when re- 
moved from the oven. Degrees 



Cent. 


Fahr. 


Rare Medium 
Rare 


Well Done 




1 
Cent, Fahr. 


Cent. 


Fahr. 


1 

Cent. Fahr. 


100 
120 
140 
160 
180 


212 
248 
284 
320 
356 


53 127.4 
51 123.8 
49 120.2 
46 114.8 
43 109.4 


63 
61 
59 

57 
55 


145.4 
141.8 
138.2 
134.6 

131.0 


75 167.0 
73 163.4 
72 161.6 
71 159.8 
70 158.0 




Highest inner temperature of the roast 
after removing from the oven. 




55 


131.0 


65 


149.0 


75 167.0 



A copper-constantan thermo-couple, as described in a preceding 
chapter, was used to measure the temperature inside the roasts. The 
thermo-couple was connected to the recording galvanometer which gave 
a continuous record of the temperature at the center of the roast. 
Fig. 17 shows some of these curves reproduced on rectangular co-ordi- 
nates. Altho these curves do not have a direct bearing on the prob- 
lem in hand, they are given here as they may be of some interest 
in other cooking investigations. 

The authorities on meat cooking recommend that a roast be cooked 
for the first ten or fifteen minutes at an oven temperature of 250?C. 
(482°F.) so as to sear the outside of the meat. The theory is that 
the coagulation of the outer surface of the meat will act as a seal to 
keep in the meat juices. A consideration of the heating curves of the 
electric ovens, discussed in the first part of this paper, shows that to 
heat an oven up to 250°C. and keep it there for fifteen minutes will 
increase the cost of electricity for roasting the meat about 50 per 
cent. In order to reduce this extra cost of energy another method was 
tried which proved very successful. Instead of searing the meat in an 
oven at a high temperature it was seared on top of the stove or rather 
by placing it in an aluminum dish over an 880-watt heating coil. The 
current was turned on for three minutes to get the dish quite hot The 
meat was then placed in the hot dish and seared for ten minutes, being 
turned frequently so as to sear all sides. 



THE ECONOMICS OF ELECTRIC COOKIXG 



29 



After searing, an incision was made in the roast with a sharp 
narrow-bladed knife, and the thermo-couple was inserted as near as 
possible in the center of the large muscle of the roast. The roast 
was then placed in the oven at the required temperature. Placing the 
roast in the oven lowered the temperature from 10 : to 20 - C. (18° to 
36 : F.). The full current of the oven was then turned on and in two 
to five minutes the temperature of the oven had again reached the 




50 



IOO 



150 200 

MINUTES 



250 



300 



required value. During the remainder of the test the current in the 
oven was varied by means of a rheostat so that the temperature re- 
mained constant within 2 C C. (3.6 : F.) of the desired value. 

When the temperature inside the roast indicated the meat to be 
cooked rare, the time and watt-hour readings were recorded. This 
was also done for medium rare and well done. As soon as the inside 
temperature indicated the meat to be well done, the roast was taken 



30 



UNIVERSITY OF MISSOURI BULLETIN 



out of the oven and left on a shelf in front of the oven, the leads of 
the thermo-couple being long enough so that it could still be left in- 
side the meat. The meat was allowed to stand until after the temper- 
ature had reached its maximum value. It was then weighed and 
put on ice until the next day when it was cut into and examined. 

Table IV. gives the time of cooking of the roasts for rare, medium 
rare, and well done. The average values lie close to smooth curves as 




shown in Fig. 18. It will be noticed that at an oven temperature of 
160°C. (320°F.) the roasts are cooked in a shorter length of time 
than at 1S0°C. (356 C F.). This is probably due to the fact that the 
slightly charred surface of the meat is a poorer conductor of heat. 
For the well-done roasts the time of cooking increases rather rapidly 
as the temperature decreases. This is not a disadvantage, however. 
if the proper temperature can be obtained automatically without the 
attention of the cook. 



THE ECONOMICS OF ELECTRIC COOKING 31 

Table IV. 



Temp, o 


: oven 


Time < 


3f cooking 


of meat roasts in minutes 


Cent. 


Fahr. 


Rare 


Average 


100 
120 
140 
160 
180 


212 
248 
284 
320 
356 

212 
248 
284 
320 
356 

212 
248 
284 
320 
356 


121 

107 

99 

53 

80 


122 
89 
76 
71 

58 


120 
97 
71 
67 
53 


121 
98 
82 
64 
63 




Medium Rare 




100 
120 
140 
160 
180 


162 
139 
111 
75 
105 


176 

114 

89 

91 

82 


170 
124 
106 

86 

75 


169 
126 
102 

84 
88 




Well Done 




100 
120 
140 
160 
180 


241 1 260 
177 165 
151 124 
164 120 
135 ' 105 


248 
172 
132 
113 
113 


250 
171 
136 
112 
118 



I 

111 
5 30 



20 




EFFECT OF OVEN TEMPERATURE 
ON LOSS IN WEIGHT OF RIB ROAST. 



IOO 
OVEN 



IZO 140 

TEMPERATURE. IN 



160 
DEGREES 



ISO 
CENT. 



32 



UNIVERSITY OF MISSOURI BULLETIN 



Table V gives the weights of the roasts before and after cooking 
and the per cent loss in weight due to the cooking. The average 
values of the per cent loss in weight of the roasts in cooking are 
plotted in Fig. 19. It will be noticed that the per cent loss in weight 
of the roasts increases with the temperature. The curve shows that 
in cooking a well-done roast so far as losses are concerned, meat is best 
when cooked between 100° and 120 C C. (212'- and 248 C F.) or possibly 
lower. 

Table V. 



Temp, of 


oven 


Weight 
before 
cooking 
Grams 


Weight 
after 
cooking 
Grams 


Li iss 

in 

weight 


Per cent 
loss in 

weight 


Average 
per cent 


Cent. 


Fahr. 


loss 


100 


212 


1904 
1600 
1760 


15(i2 
1288 
1392 


4(i2 
512 
368 


21.1 
19.5 
20.9 


2o.5 


120 


248 


1580 
1782 
1824 


1270 
1380 

1454 


310 
402 
390 


19.6 

21.4 


21.2 


140 


284 


1700 
1900 
1820 


1552 
1492 

1414 


348 
408 

406 


20.5 
21.5 
22.3 


21.4 


160 


320 


1554 
1612 
1566 


1160 
125 7 
1182 


5<)4 


23.2 
24.5 


24.5 


180 


356 


1628 
1832 

IS 14 


12 20 
1555 

15HU 


408 

49 7 
514 


25.1 

2 7. 1 




200 


392 


1805 


1244 


561 


51.0 


51.0 



As the proper facilities were not available, no attempt was made 
to analyze the drippings obtained at the various temperatures to de- 
termine the proportion of water, protein, and fat. The appearance of 
the drippings, however, would indicate that there is a larger pro- 
portion of fat in the drippings obtained at the high oven temperatures 
than at the low temperatures. 

The other important factor which determines the best roasting 
temperature is the cost of the electricity used. As an aid to clearness 
in determining the most economical roasting temperature the total 



THE ECONOMICS OF ELECTRIC COOKIXG 



33 



energy used in cooking the meat "will be divided into several com- 
ponents and each will be discussed separately. 

As mentioned before the roasts were first seared over an open 
heating coil. This operation required 880 watts for 13 minutes or 
190 watt-hr. and was the same for all the roasts. 

Part of the total energy was used in heating the oven from room 
temperature to the temperature required for the cooking. This was 
done before the roast was put in the oven and is commonly known 
as preheating. The amount of energy required for this purpose, as 
shown in a preceding paragraph, depends upon the construction of the 
oven and the size of the heating coil. The curves of Fig. 12 show the 
energy required for the ovens tested. 

If food is placed in an oven after the oven is heated to a certain 
temperature, the temperature will decrease, due partly to the heat 
lost by opening the door and partly to the heat absorbed by the cold 
utensil and food. To bring the temperature of the oven up to its 
former value additional energy will have to be supplied. The term 
afterheating will be used in this paper to distinguish this heating 
of the oven after food is inserted from the heating of the oven before 
the food is placed in it. 

In the meat experiments the energy used in afterheating was 
determined. As soon as the meat was placed in the oven the current 
was turned on full until the temperature of the oven had increased 
to its original value. The reading of the watt-hour meter was then 
taken. The watt-hours thus determined are given in column 3 of Table 
VI for the various oven temperatures. 

Table VI. 



Oven temperature Watt-hours required to bring Watts required to 

oven temp, to former value maintain the oven and 

roast at constant tern- 



Cent. 


Fahr. 




perature. 




100 


212 


44 




249 


120 


248 


67 




321 


140 


284 


75 




395 


160 


320 


114 




485 


180 


356 


156 




586 



The variation of this energy with the oven temperature is shown 
by curve A in Fig. 20. The time required for the oven temperature 
to attain its former value after the roast was inserted varied from 
two to five minutes. During this time part of the energy supplied was 



34 



UNIVERSITY OF MISSOURI BULLETIN 



lost by conduction thru the insulation and around the throat as ex- 
plained in a preceding paragraph. As this heat loss thru the walls of 
the oven is known for a particular temperature, the energy measured 
by the watt-hour meter (curve A Fig. 20) can be corrected by subtract- 
ing the energy lost thru the walls during the time required for the 
afterheating. Curve B Fig. 20 shows these corrected values. The 



I40 



3 
O 

r 



IOO 



60 



«»o 



FIG. 20 
CURVE A : ENERGY REQUIRED TO BRING OVEN UP 
TO FORMER TEMPERATURE AFTER 
MEAT IS INSERTED. 
CURVE B: SAME AS A, CORRECTED FOR RADIA- 
TION! i n<%* Awn npFwiNf-, nnno 








I- 












/ 












/ 












/ 

/ 












/" 












/ 


























_> 













SO IOO ISO 200 250 

OVEN TEMPERATURE. IN DEGREES CENT 



ordinates of this curve are a measure of the energy used in afterheat- 
ing at the various oven temperatures. 

After the temperature of the oven has attained the desired value 
the energy supplied to maintain this temperature is practically con- 
stant. Since the cooking of a roast consists in raising its temperature 
to 60°C. (140°F.) or above, there is a constant supply of heat energy 
to the meat. Part of this is used in increasing the internal temper- 
ature of the meat and part is used in vaporizing the water and other 



THE ECONOMICS OF ELECTRIC COOKING 



35 



volatile matter of the meat. Column 4 of Table VI gives the watts 
required to maintain the oven and roast at a constant temperature. 
Curve A Pig. 21 shows these values of watts plotted against oven tem- 
perature as abscissas. For the sake of comparison a similar curve for 
the empty oven is here repeated. The difference between these two 
curves is the energy absorbed by the meat either in increasing its 
temperature or vaporizing its moisture. 



eoo 



50O 



5400 

o 

r 

h 

I 300 



100 



Fie. si 

ENERGY REQUIRED TO MAINTAIN 
OVEN AT CONSTANT TEMPER- 
ATURE WITH ROAST IN OVEN; 
AND EMPTY. 




30 



25 



20 



15 



IO 



OVEN 



SO IOO 150 

TEMPERATURE. IN 



200 
DEGREES 



250 
CENT. 



Consideration of these curves leads to a method of determining 
the ratio of the heat units absorbed by the food to the total heat 
units supplied. Since the ordinates of curve B represent the energy 
required to maintain the oven at a constant temperature when empty 
and the ordinates of curve A represent the energy required to maintain 
the oven at a constant temperature after the roast is placed therein; 
the difference between the two may be taken as a measure of the 



36 



UNIVERSITY OF MISSOURI BULLETIN 



energy actually absorbed by the food. In other words the difference 
between the ordinates represents the energy output of the oven. There- 
fore, for any oven temperature the ordinate of curve A minus the 
ordinate of curve B divided by the ordinate of curve A would equal 
the efficiency of the oven when roasting beef. Curve D of Fig. 21 
gives the values of the efficiency obtained by this method. Even if 




FI6. 22 
ENERGY REQUIRED TO ROAST 
BEEF IN OVEN NO. I .STARTING 
WITH OVEN HOT. BRAIZING 
190 WATT-HOURS ADDITIONAL. 



100 
OVEN 



120 I ao 160 

TEMPERATURE IN DEGREES 



the best accuracy were obtainable by this method it does not tell much 
about the actual cost of roasting meat. It well emphasizes the fact, 
which was discussed in a previous paragraph, that the method of 
measuring the efficiency of a steam boiler is not adaptable to cooking 
apparatus. According to the curve just obtained, the energy required 
for roasting beef at 180°C. (356°P.) ought to be loss than at lower 
temperatures. Quite the contrary is true, however. At 180°C. more 
heat units are absorbed by the meat than at lower temperatures, but 



THE ECONOMICS OF ELECTRIC COOKING 



37 



this excess of beat in the meat is detrimental to its quality. The 
extra amount of heat is used to cause a larger loss in weight of the 
meat as shown by the curve in Fig. 19. It also chars the outside of 
the meat, forming a heavy crust which is very indigestible. 

The curves of Figs. 22, 23, and 24 give the energy used in roasting 
beef in ovens Nos. 1, 2, and 4, starting with the oven 1 at the required 
temperature. The energy used in braizing (or searing) the roasts is 



80O 



700 



geoo 

3 


I 

jlsoo 

1 

-400 



300 



200 



FIG. 23 
ENERGY REQUIRED TO ROAST 
BEEF IN OVEN NO. E.STARTINS 
WITH OVEN HOT. BRAIZING 
190 WATT-HOURS ADDITIONAL 




IOO 120 I40 ISO ISO 

OVEN TEMPERATURE IN DEGREES CENT. 



not included in the ordinates to these curves, since it was the same 
in all cases, 190 watt-hours. It will be noticed that for rare roasts 
100°C. (212°F.) is the most economical temperature in all the ovens, 
and for medium rare 100 °C. is the most economical temperature ex- 
cept for oven No. 1 for which 120°C. to 140°C. (248°F. to 284°F.) is 
the best. The difference in this case is very slight, however, and 
within the probable error so that 100 °C. could be used economically 



38 



UNIVERSITY OF MISSOURI BULLETIN 



even here if desired. For the well-done roasts there is a decided 
difference in the cost of cooking the meat at the various oven temper- 
atures. For all the ovens the most economical temperature for the 
well-done roasts lies between 120° and 140 °C. 

"When it is necessary to heat up the oven from room temperature 
different curves are obtained as shown in Figs. 25, 26, and 27. It 



600 



SOO 

8 

O*oo 

I 
h 

£ 300 



200 



IOO 



ENERGY REQUIRED TO ROAST 
BEEF IN OVEN NO.4, STARTING 
WITH OVEN HOT. BRAIZING 
190 WATT-HOURS ADDITIONAL.. 




IOO 120 iAO 

OVEN TEMPERATURE. IN 



ieo 

DEGREES 



ISO 
CENT. 



will he noticed that the rare and medium rare curves are much 
steeper and the difference in cost in favor of 100 C C. is greater. For 
ovens No. 1 and 2 120 °C. (248°F.) is the most economical temperature 
for well-done roasts while for oven No. 4, 100 °C. is the best. With 
the cost of electricity at 5 cents per kilowatt-hour for oven No. 1 the 
difference between the cost of roasting meat at 100°C. and at 180°G. 
is 2 cents for rare, 2% cents for medium rare, and for well-done the 
difference between 120°C. and 1S0°C. is 2% cents. The saving in the 



THE ECONOMICS OF ELECTRIC COOKING 



39 



month's bill for the average family would probably amount to about 
50 cents. It is well worth considering, however, since by observing 
these economies electric cooking will be able to compete with the 
cheaper fuels. 

It will be noticed that the energy required for roasting meat in 
oven No. 1 is considerably greater than in ovens No. 2 and 4. This 
is due partly to the smaller amount of heat insulation used and partly 



IBOO 



1600 



1400 



rt» 200 

K 

D 

I IOOO 

I 

I- 

t BOO 



60O 



400 



EOO 




FIG. 25 
ENER6Y REQUIRED TO 
ROAST BEEF IN ON/EN NO. I. 
PREHEATING INCLUDED. 
BRAIZING 190 WATT-HOURS 
ADDITIONAL-. 



IOO 120 14-0 

OVEN TEMPERATURE IN 



160 
DEGREES 



ieo 

CENT. 



to the larger size of the oven. The oven was much larger than was 
necessary for cooking this size of roast. On this account both the 
radiation losses and the preheating loss were much greater than in the 
smaller ovens. 

The energy curves just described were obtained in the following 
manner: The radiation loss was calculated for. the required time of 
cooking. To this was added the loss due to opening the door and the 



40 



UNIVERSITY OF MISSOURI BULLETIN 



energy absorbed by the meat as given by the curves of Fig. 20 and 21. 
The values thus obtained were checked for 100°C. (212 °F.) and 160°C. 
(320°F.) by cooking roasts at these temperatures in ovens No. 2 and 
4. Oven No. 3 was tried at 160 °C. but the heating element was found 
inadequate to maintain the required temperature in the oven after 
the roast was placed therein. The energy curves for this oven were 
therefore not obtained. 



Fie. 26 
ENERCbY REQUIRED TO ROAST 
BEEF IN OVEN NO. 2. PRE- 
HEATING INCLUDED. BRAIZING 
190 WATT-HOURS ADDITIONAL 




IOOO 



Irt 800 

D 
O 

I eoo 
i 

h 



200 



IOO 120 14-0 ieo ISO 

OVEN TEMPERATURE IN DEGREES CENT. 

An experiment was tried by braizing the roast in the manner 
recommended by the cook books. The oven was heated to 250 C C. 
(482 °P.) the roast was placed therein, and full current was turned on 
until the temperature had returned to the desired value. The current 
was then turned off and the oven allowed to cool down to 106°C 
(212 °F.) where it was kept constant during the remainder of the 
experiment. The energy required for preparing the roasts by both 
methods is given in the following table: 



THE ECONOMICS OF ELECTRIC COOKING 

Table VII. 



41 



Watt-hours used in preparing roasts by the two methods of searing 



Searing on 
top coil 


Remainder 

of test in 

oven at 

100 °C. 

(212 °F.) 


Total 


Total when 

seared in 

oven 


Difference 


Rare 190 

Well done.... I 190 


790 
1325 


880 
1515 


1950 

2580 


1070 
1065 



The saving in energy in favor of searing on top of the stove is 
surprisingly great, making a difference of 5 cents (at five cents per 







E.NE.RGV 
pap~p-ir* iri_ 


Fie. 2.7 
' REQUIRED 


TO 


ROAST 








HELATfNCb INCLUDED. BRAIZING 
190 WATT-HOURS ADDITIONAL. 


























BOO 




































48$ 


■A 


» 


3 ©OO 

O 

r 
i 


< 










\N* 


^ 


OjZ>s* 






£ 400 

1 

200 


p 


. . 1 OOkf 


IE J 






med 
*~~rp^ 







































IOO \ZO \A-0 IGO ISO 

OVEN TEMPERATURE. IN DEGREES CENT 



42 UNIVERSITY OF MISSOURI BULLETIN 

kw-hr.) in the cost of preparing the roast. This great difference in 
the energy used by the two methods is due to the fact that when sear- 
ing the meat in the oven the whole oven had to be heated up to the 
high temperature of 250 °C. (482°F.) resulting in large preheating and 
radiation losses, while by the other method only the heating element, the 
dish, and the outside surface of the roast are heated to the high tem- 
perature. The losses are consequently greatly reduced. 

Boiling meats. Electric insulated ovens of the proper construc- 
tion are particularly adapted to boiling meats or rather cooking in 
water at the desired temperature. This process requires a long time 
and a low degree of heat. 

The researches of Grindley * have disposed of the theory that meat 
should be first placed in water at the boiling temperature for ten 
minutes to seal up the outside. He says, "Thoro investigation confirms 
the conclusion that when meat is cooked in water at from 80° to 
85°C. (176° to 185°F.), placing the meat in hot or cold water at the 
start has little effect on the amount of material found in the broth." 
The most economical method of boiling by means of electricity is, 
therefore, to immerse it in water and place it in the oven without pre- 
heating. If a small well-insulated oven is used and the dish placed 
directly on the heating element without a baffle, the meat can be 
cooked by using only a small amount of electricity. 

Experiments on the temperature of coagulation of proteid and the 
decomposition of oxyhaemoglobin, the red coloring matter of meat, in- 
dicate that the probable lowest temperature of cooking meat is in the 
neighborhood of 75 °C. (167°F.). One hundred degrees centigrade, the 
boiling point of water, will be the highest temperature used and the 
most economical temperature will be somewhere within this interval. 

The increased popularity of the tireless cooker indicates that people 
are learning that food can be cooked below the boiling temperature 
and that meat is more tender and appetizing when cooked at 80 C C. 
than at 100 °C. as shown by many experiments. Cheap cuts of meat 
can be used and sometimes made nearly as attractive as the more 
expensive cuts cooked in the ordinary way. 

No experiments were undertaken on cooking meats in water, hence 
no definite data can be given as to the amount of electricity required 
for such cooking. 

BAKING EXPERIMENTS 
Owing to a lack of definite information on the time and tempera- 
ture of baking, a series of experiments were undertaken on the baking 
of biscuit, bread, and sponge cake. The purpose of the experiments 



1. Losses in Cooking Meat, U. S. Dept. of Ag. Bui. No. 141. p. 95. 



THE ECONOMICS OF ELECTRIC COOKING 



43 



was to determine the range of temperatures within which each article 
of food could be satisfactorily baked and the particular temperature 
within this interval which was the most economical for the ovens 
tested. 

The method used was to determine the minimum time of baking 
at several oven temperatures. The experiments at a particular tem- 
perature were started at what was thought to be the proper time of 
baking at that temperature. If the condition of the food was well done 
and well browned the time of baking was reduced. This process was 
repeated until under-done samples were obtained. The shortest time 
of baking which gave satisfactory results was taken for that particular 
temperature. This was repeated for several oven temperatures and 
curves were plotted between the temperature of oven and the minimum 
time of baking. Each sample was carefully weighed before and after 
baking and the per cent loss of weight determined. The per cent loss 
of weight obtained at the minimum time of baking was then plotted 
against the oven temperature. Each point obtained on this curve was 
the mean of three determinations. The experiments were first per- 
formed in Oven No. 1 and were then checked in the other ovens. 

Because of the short time of cooking and the small amount of 
food used in each sample it was not found possible, as in the meat 
experiments, to get accurate measurements of the amount of heat 
absorbed by the food. Consequently the amount of energy used 
in baking at the various temperatures in each oven was taken as the 
sum of the losses. 



20 



15 



U 

a 



Fie. 28 
EFFECT OF OVEN TEMPER- 
ATURE ON TIME OF BAKING 
BISCUITS AND PER CENT 
LOSS OF WEIGHT 




OVEN 



160 IGO 

TEMPERATURE. 



220 240 

CENTIGRADE. 



44 



UNIVERSITY OF MISSOURI BULLETIN 



Fig. 28 shows the minimum time of baking and the per cent loss 
in weight curves for biscuits. Each sample consisted of six biscuits, 
the total sample weighing approximately 25 grams. They were pre- 
pared according to the following recipe: 
1 cup of flour, 

1 tablespoonful of lard, 
y 2 teaspoonful of salt, 

2 teaspoonfuls of baking powder, 
enough milk to make a soft dough. 

It will be noticed from the curves that the per cent loss of weight 
begins to increase very rapidly as the temperature decreases below 
200°C. (392°P.). This increase in the loss of weight of the biscuits 
at the low temperatures indicated that the samples dried out to a 
greater extent due to the increased time of baking. This was very 
evident in the character of the biscuits prepared at these temperatures. 
They were dry and hard and had a heavy crust, instead of being crisp 
and tender. At 200 °C. and above there was no difference discernible 
in the character of the samples. The range of temperature, there- 
fore, for baking biscuits prepared according to the above recipe is 
from 200° to 240°C. (392° and 464°F.). Table VIII which gives in 
detail the results of the biscuit experiments will make clear the 
method used. 




160 iso eoo 220 2ao 

oven temperature: in degrees centigrade 

Fig. 29 shows the minimum time of baking and the per cent loss 
of weight curves for the bread experiments. The loaves averaged 
300 grams in weight and were baked in a tin the dimensions of which 
were 3 inches by 5 inches by 3 inches deep. The bread was prepared 
according to the following recipe: 



THE ECONOMICS OF ELECTRIC COOKING 
Table VIII — Biscuit Experiments 



45 





Oven tem 


perature 






Time of 






Percent loss 
of weight 


Condition of sample 


baking 










Cent. 


Fahr. 






Minutes 










10 


239.5 


463.1 


15.8 


well done, well brown 


10 


239.5 


463.1 


15.5 


well done, well brown 


10 


240.0 


464.0 


15.9 


well done, well brown 


8 


239.5 


463.1 


12.9 


well done, well brown 


8 


239.0 


462.2 


14.9 


well done, well brown 


8 


240.0 


464.0 


13.0 


well done, well brown 


7 


241.0 


465.8 


10.1 


slightly brown, doughy 


7 


240.5 


464.9 


10.8 


slightly brown, done 


7 


240.0 


464.0 


10.1 


slightly brown, almost done 


10 


220.0 


428.0 


13.0 


well done, well brown 


10 


221.0 


429.8 


12.9 


well done, well brown 


10 


221.0 


429.8 


14.4 


well done, well brown 


10 


220.0 


428.0 


14.3 


well done, well brown 


9 


220.0 


428.0 


12.9 


not brown, doughy 


9 


221.0 


429.8 


12.2 


slightly brown, done 


12 


195.0 


383.0 


14.2 


well done, well brown 


12 


194.0 


381.2 


15.1 


well done, well brown 


12 


196.0 


384.8 


15.9 


well done, well brown 


10 


195.0 


383.0 


8.0 


slightly brown, done 


10 


195.0 


383.0 


7.2 


slightly brown, almost done 


11 


195.0 


383.0 


15.0 


well done, slightly brown 


11 


195.0 


383.0 


13.6 


almost done, brown 


11 


195.5 


383.9 


14.6 


almost done, slightly brown 


14 


180.0 


356.0 


17.8 


well done, well brown 


14 


180.5 


356.9 


19.2 


well done, well brown 


14 


180.0 


356.0 


18.8 


well done, well brown 


13 


180.0 


356.0 


13.0 


slightly brown, almost done 


13 


180.0 


356.0 


11.6 


well done, well brown 


13 


180.5 


356.9 


14.3 


brown, almost done 


15 


170.0 


338.0 


17.0 


almost done, not brown 


15 


170.0 


338.0 


16.5 


almost done, not brown 


15 


170.0 


338.0 


16.2 


almost done, slightly brown 


16 


170.5 


338.9 


10.7 


done, slightly brown 


16 


170.5 


338.9 


13.3 


done, slightly brown 


16 


169.5 


337.1 


12.7 


almost done, slightly brown 


17 


170.0 


338.0 


20.9 


well done, brown 


17 


170.0 


338.0 


20.2 


well done, brown 


17 


170.0 


338.0 


21.2 


well done, brown 



V 2 cup of water, 

% cup of milk, 

1 teaspoonful of lard, 

% teaspoonful of salt, 

1 tablespoonful of sugar, 

enough hard wheat flour to make a soft dough, 

yeast. 



46 



UNIVERSITY OF MISSOURI BULLETIN 



In the bread experiments the most satisfactory results were ob- 
tained above 180°C. (356°F.). At the lower temperature the crust 
was hard and thick due to excessive evaporation of moisture as indi- 
cated by the loss in weight curve. At 240 °C. (464°F.) the outside of 
the loaf had a tendency to brown over before the inside was thoroly 
done. So many factors other than the time and temperature of baking 
affect the texture and quality of the bread that no attempt was made 
to accurately score the loaves baked. The quality of flour, the propor- 
tion of the ingredients, and the manipulation before baking * all affect 
the flavor, quality, and texture of the loaf. It may be stated, how- 
ever, that the range of temperature for baking bread in the above sized 
loaves lies between 180° and 240 °C. The size of pan used was smaller 
than is used in the average household and the time required for 
baking a larger loaf would be somewhat longer. 



FIG.30 
EFFECT OF OVEN TEMPER- 
ATURE. ON TIME OF BAKIN& 
SPONGE CAKE AND PER- 
CENT LOSS OF WEIGHT. 




3 

Oh 



160 170 

TEMPERATURE 



ISO 
DEGREES 



190 200 

CENTIGRADE 



Fig. 30 shows the minimum time of baking and the per cent loss 
of weight curves for the sponge cake tests. The cake was prepared 
according to the following recipe: 

4 eggs, 

1 cup of sugar, 

1 cup of flour, 

1 tablespoonful of lemon juice. 



1. Univ. of 111. Bull. Vol. X, No. 25. 



THE ECONOMICS OF ELECTRIC COOKING 



47 



The loaves averaged 250 grams in weight and were baked in a 
tin dish of the following dimensions: 5.5 inches by 4.2 inches by 2.5 
inches deep. 

The lowest temperature that should be used for baking sponge 
cake is approximately 170 °C. (338°F.) as the crust becomes very 
heavy and thick at the lower temperatures due to the long baking and 



FIG. 31 
ENERGY REQUIRED TO BAKE 
BISCUITS, STARTING WITH OVEN 
COLD AND WITH OVEN HOT. 




900 



800 



TOO 



g 600 

D 


, BOO 

h 

\ 

§ 400 



300 



200 



IOO 



160 ISO 200 22 O 2<40 

OVEN TEMPERATURE IN DEGREES CENT. 

the large loss of moisture. Because of the larger proportion of liquid 
in the dough, sponge cake will stand a greater loss of moisture than 
bread or biscuits. At 200°C. (392°F.) the loss of moisture was evi- 
dently too small as the texture of the crumb was not as good as the 



48 



UNIVERSITY OF MISSOURI BULLETIN 



samples baked at lower temperatures. The range of temperature, 
therefore, for baking sponge cake lies between 170° and 200 °C. (338° 
and 392°F.). 

The curves of Fig. 31 show the amount of energy used in baking 
biscuits at the various oven temperatures for ovens Nos. 1, 2, and 4 
with and without preheating. The curves show that if biscuits are 
baked immediately after other food is removed from the oven so that 
preheating is not necessary the energy required will be very small 
compared to the amount required if the oven has to be heated up from 
room temperature to baking temperature. This is especially true of 




I80 200 220 

TEMPERATURE IN DEGREES 



2AO 
CENT. 



oven No. 1. When the baking is begun with the oven already at the 
desired temperature, the energy used in baking biscuits is practically 
the same for all the temperatures tried: but when the oven has to be 
heated up from room temperature the energy used is considerably less 
at the lower temperatures. Since the quality of the biscuits baked at 
temperatures balow 200°C. (392°P.) is not as satisfactory as at higher 



THE ECONOMICS OF ELECTRIC COOKING 



49 



temperatures, these temperatures are not recommended. Two hundred 
degrees Centigrade is, therefore, the most economical temperature for 
baking biscuits when preheating is necessary. 

Because the conditions of baking biscuits satisfactorily are a high 
temperature for a short time, the greater part of the energy required 
will be used in preheating. Consequently ovens used for baking bis- 
cuits should require as little energy as possible for preheating. This 



o soo 
or 

D 

8 

* 700 

i 

£ 600 



FIS 33 
ENERGY REQUIRED TO 
BAKE BREAD, -STARTING - 
WITH OVEN COLD. 




160 ISO 200 

OVEN TEMPERATURE. 



220 
DEGREES 



can be accomplished to a certain extent by using as small an oven as is 
practical. 

Biscuit samples were also baked in ovens Nos. 2, 3, and 4. In 
oven No. 2 the biscuits did not brown satisfactorily on top as there 
was no heating element in the top of the oven. Oven No. 3 was found to 
be unsatisfactory for baking biscuits because with the heating arrange- 
ment used it was difficult to get sufficiently high temperatures. The 



50 



UNIVERSITY OF MISSOURI BULLETIN 



biscuits baked in oven No. 4 were quite satisfactory. The time of 
baking and the per cent loss of weight checked with the values obtained 
for oven No. 1. 

The curves of Fig. 32 show the amount of energy used in baking 
bread at the various oven temperatures without preheating. It will be 
noticed that for all the ovens the energy required is a minimum above 



GOO 



500 

if) 

K 

D 

4OO 

i 

h 

<C 300 



200 



IOO 



ENERGY REQUIRED TO 
BAKE SPON€>E CAKE, 
STARTING WITH OVEN HOT. 




160 ITO I80 190 ZOO 

OVEN TEMPERATURE IN DEGREES CENT. 



220°C. (428°F.). The most economical temperature for baking bread 
when the oven is already heated is, therefore, from 220 ° to 240 C C. 
(428° to 464°F.). 

The curves of Fig. 33 show the amount of energy used in baking 
bread at the various oven temperatures including preheating. The 
temperature for which the energy required becomes a minimum lies 
between 200° and 215°C. (392° to 419 °F.) depending on the oven 



THE ECONOMICS OF ELECTRIC COOKING 



51 



used. Altho the insulation of oven No. 4 is very much better than 
that of oven No. 2, it will be noticed that above 205 °C, oven No. 4 
requires more energy for baking bread than oven No. 2. This is due 
to the larger amount of energy required for the preheating. 

The curves of Pigs. 34 and 35 show the amount of energy used 
in baking sponge cake at the various temperatures with and without 




700 
600 

r 
i 

\- 

5 500 



.400 




FIG. 35 
ENERGY REQUIRED TO BAKE 
SPONGE CAKE, STARTING 
WITH OVEN COLD I 

I I I 



160 170 ISO 190 200 

OVEN TEMPERATURE. IN DEGREES CENTIGRADE 



preheating. As shown by the curves, the most economical tempera- 
ture for baking sponge cake, when the oven is already heated, is 
200 °C. Except for oven No. 4 this is also the most economical tempera- 
ture when the oven is started at room temperature. For oven No. 4, 
the most economical temperature is 180 °C. but the difference in the 
energy required at 180° and 200 °C. is slight. Because of the poorer 
quality obtained at 200 °C, the best temperature for baking sponge 
cake will be between 180° and 190 °C. 



52 UNIVERSITY OF MISSOURI BULLETIN 

Consideration of the baking curves as a whole will emphasize the 
importance of the preheating characteristics in designing an efficient 
electric oven. For the kinds of baking which require a high tempera- 
ture for a short time the preheating loss is considerably greater than the 
radiation and convection loss. Unless some method can be found for de- 
creasing the energy used in heating the oven up from room tempera- 
ture it will not be practical to increase the heat insulation of the ovens 
used for domestic baking. This does not apply, however, to ovens 
which are used for long intervals at the same temperature. 

THICKNESS OF HEAT INSULATION 

If a heat insulating material is placed between the inner and the 
outer surfaces of an electric oven, the radiation and convection losses 
will be reduced, due to the lower temperature of the outside surface, 
as explained in a previous paragraph. For the same internal temper- 
ature of the oven, the greater the thickness of insulation used, the 
lower will be the temperature of the outside surface and the smaller 
will be the losses. It would not be economical, however, to increase 
very greatly the thickness of the heat insulation as the cost of each 
additional inch increases rapidly and the effect of each additional inch 
on the amount of energy lost decreases even more rapidly. If, for a 
given insulating material, the number of hours per year that the oven 
will probably be used at the various oven temperatures and the cost 
of electricity are known, there is, evidently, a definite thickness of 
heat insulation for which the sum of the cost of the energy lost per 
year due to the radiation and convection and the annual cost of the 
insulation will be a minimum. 

In order to obtain some data on the most economical thickness 
of heat insulation for electric ovens a series of experiments were under- 
taken. From one to eight inches of powdered kieselguhr was used 
for the heat insulation. A heating element and a thermo-couple were 
placed in a tin box 9 inches by 10.5 inches by 12 inches, which were the 
inside dimensions of ovens Nos. 2 and 4. This box was placed inside 
a larger box and the space between the two was filled with the insu- 
lating material. Care was taken to center the inner box accurately 
so as to obtain a uniform thickness of insulation on all sides. The 
insulation was packed gently and uniformly so that the density ob- 
tained was approximately twenty pounds per cubic foot. 

The method used in each test was to connect the heating element 
to a source of constant potential and leave it until the inside tem- 
perature of the oven reached a constant value, when readings were 
taken of watts input and the oven temperature. 

A copper constantan thermo-couple which had been calibrated by 
the Bureau of Standards was used to measure the oven temperature. 



THE ECONOMICS OF ELECTRIC COOKING 



53 



During the first part of each test it was connected to a Bristol record- 
ing galvanometer. After the internal temperature had remained con- 
stant for at least three hours the thermo-couple was connected to a 
potentiometer, by means of which the e. m. f. of the couple was accu- 
rately obtained. The cold junction was kept at 0°C. (32°P.) by im- 
mersion in ice water. 

During the first few hours of each test the heating element was 
connected to the laboratory supply mains while for the last six hours 
of each test it was connected to a motor generator set, the voltage of 



i — i — r 



FIG. 36 
RADIATION AND CONVECT- 
ION LOSS FOR VARIOUS 
OVEN TEMPERATURES 




THICKNESS 



3 -4- S 6 7 © 

OF INSULATION IN INCHES 



which was kept constant by means of a Tirrill regulator. Energy 
input was obtained from the readings of a voltmeter and an ammeter 
which had been carefully calibrated by comparison with Weston labora- 
tory standards. The kind of external surface used in each test was 
new bright tin. The bottom surface rested on a cement floor. 



54 



UNIVERSITY OF MISSOURI BULLETIN 



The results of the experiments are given in Table IX since for a 
given thickness of heat insulation and low temperature of external 
oven surface the radiation and convection loss is approximately pro- 
portional to the difference between the room temperature and the 
inside temperature of the oven as shown in Fig. 11, — the loss for any 
oven temperature can be calculated. The curves of Fig. 36 show the 
relation between the thickness of insulation and the watts lost for 
oven temperatures of 100°, 150°, 200°, and 250°C. (212°, 302°, 392° 
and 482°F.). 



6.00 



3.O0 



(0 

< 

J 
J 


Q3.00 



I.OO 





FIG. 37 
CURVES SHOWING MOST 








ECONOMICAL THICKNESS 
OF HEAT INSULATION. 

1. ANNUAL. COST OF ENER6Y LOST 
THRU INSULATION AT$.05 PER KW-HF 

2. ANNUAL COST OF INSULATION, 
INCLUDING ADDED COST OF OVEN 

3. SUM OF 1 AND 2. 






\ 


























I 


\ 




















V 












/ 


> 






A 


u 


i ! , 




3^< 




















/ 




/ 


► 














3^ 






i 

























I 2 

THICKNESS 



3 A 5 6 T 

OF INSULATION IN 



INCHES 



If the number of hours per year that an oven of this size will be 
used at the various oven temperatures can be estimated, the cost per 
year of the radiation and convection losses can be calculated from 
these curves. In order to get a value for the most economical thick- 
ness of heat insulation, it is assumed that an oven of this size is to be 
used as follows: 



THE ECONOMICS OF ELECTRIC COOKING 



55 



100 


hr. 


per 


yr. 


at 


200°C. 


(392°F.) 


150 


hr. 


per 


yr. 


at 


175°C. 


(347°F.) 


400 


hr. 


per 


yr. 


at 


150°C. 


(302°F.) 


750 


hr. 


per 


yr. 


at 


125°C. 


(257°F.) 



It is also assumed that the cost of electricity for cooking is 5 cents 
per kilowatt-hour. 

Curve 1, Fig. 37 shows the cost per year of the radiation and con- 
vection loss for various thicknesses of insulation. Curve 2 shows the 
cost of heat insulation used, at 2 cents per pound and twelve pounds 
per <mbic foot. An accurate expression for the cost of adding extra 
insulation should include the extra cost of the outside covering of the 

Table IX. 



Thickness of 
insulation, in. 



Internal temp, 
degrees 



Room temp, 
degrees 



Cent. 



Fahr. 



Fahr. 



Watts 
loss 



8 
8 


271.1 
271.0 


520.0 
519.8 


24 

25 


75.2 
77.0 


67.4 
67.4 


6 
6 


270.5 
271.0 


518.9 
519.8 


27 
26 


80.6 
78.8 


70.6 
71.0 


4 
4 


233.1 
237.8 


451.6 
460.0 


25 
25 


77.0 
77.0 


71.2 
71.4 


3 
3 


210.4 
210.2 


410.7 
410.4 


26 

27 


78.8 
80.6 


71.7 
71.7 


2 
2 


170.6 
171.8 


339.1 
341.2 


25 
25 


77.0 
77.0 


69.4 
72.1 


1 
1 


106.5 
106.3 


223.7 
223.3 


24 

25 


75.2 
77.0 


67.6 
67.5 



oven, necessitated by the extra volume of insulation. As no data are 
available to the author concerning the cost of manufacture, it is as- 
sumed that for each thickness of insulation the manufacturing cost of 
parts of the oven affected by the thickness of insulation is three times 
the cost of the insulation itself. If an interest and depreciation charge 
of 25 per cent is assumed, curve 2 becomes the cost per year of insu- 
lating this size oven with various thicknesses of heat insulation. It 
is evident that for the most economical thickness of heat insulation 
the sum of curve 1 and curve 2 should be a minimum. This condition 



56 UNIVERSITY OF MISSOURI BULLETIN 

is fulfilled for an insulation thickness of four inches as shown by 
curve 3. 

In a similar manner the most economical thickness of heat insu- 
lation for any given set of conditions can be determined. A limiting fac- 
tor other than the cost of the insulation is the rapid increase in the 
size of the oven for the larger thicknesses. It is unlikely that insu- 
lation thicknesses more than four inches will be used for domestic 
purposes; because, for thicknesses above this value, the ovens become 
too large and cumbersome to use in the ordinary kitchen. 

The results of the experiments just described indicate that a net 
annual saving would result if the commercial electric ovens now on 
the market were better insulated. There are several electric ovens 
now on the market which have as small as one inch of heat insulation. 
Even under the most favorable conditions this could probably be 
economically increased to two or three inches. 

An objection that the designer of electric ovens may bring against 
an increase in the thickness of heat insulation is the danger to the 
oven if the automatic cut off fails to operate. The ovens now on the 
market are built to withstand the highest oven temperature obtainable 
with all the coils turned on full. This design is necessary at present be- 
cause of the lack of a cheap and reliable automatic release. As an 
auxiliary to a mechanical release, a heat fuse might be constructed 
so as to melt due to the internal temperature of the oven if the me- 
chanical release failed to operate. For ovens operating at 100 ~C. 
(212°F.) or less, pure tin might be used and zinc for ovens using 
higher temperatures. Even if the retail price of such a fuse should 
be high, their use would not be prohibitive as they would blow only 
when the automatic release failed to work. 

Kieselguhr was chosen as the heat insulating material in the 
above experiments as it is the cheapest of the good heat insulators 
which will stand medium high temperatures: its melting point being 1 
1610°C. (3930°F.). 

Of other materials used for heat insulation of electric ovens silox. 
mineral wool, and non-pareil insulating brick also give good results. 
No experiments were made by the author, however, to determine the 
relative advantages of each. Cork board was used on one of the 
experimental ovens constructed; but altho it is a very good heat insu- 
lator it is not to be recommended for oven temperatures above 100°C. 
(212 °F.) on account of its combustibility. 



1. Met. & Chem. Engr.. vol. 12, p. 112. 



THE ECONOMICS OF ELECTRIC COOKING D/ 

SUMMARY 

1. The radiation and convection loss from an insulated electric 
oven can be obtained for any oven temperature below 250 °C. (482°F.) 
by measuring the maximum temperature of the oven for a given energy 
input plotting these values and drawing a straight line thru the point 
thus obtained and zero energy at room temperature. 

2. The preheating loss of an electric oven can be obtained by 
taking simultaneous readings of watt-hours and oven temperature. 
For domestic use the preheating loss should be made as small as pos- 
sible by decreasing the heat capacity of the oven as much as is prac- 
tical and by using a large coil for the preheating. 

3. The energy lost when the door of an electric oven is opened 
for fifteen seconds was determined for various oven temperatures. 
For an oven temperature of 200 C C. (392°F.) used in baking bread, 
biscuits, etc. the loss due to opening a 12-inch by 18-inch oven door 
for fifteen seconds amounted to twelve watt-hours. At 5 cents per 
kilowatt hour for electric current this would mean a cost of six one- 
hundredths of a cent each time the door was opened for a period of 
fifteen seconds. (See Fig. 15.) 

4. Since the purpose of cooking food is not to put as many heat 
units as possible into the food but is rather to improve its flavor and 
to increase its digestibility, the steam boiler method of determining 
efficiency is not applicable to electric ovens. 

5. In order to compare the cost of cooking in various electric 
ovens a method proposed for indicating the relative efficiency of the 
electric ovens is to specify the amount of the preheating and the 
radiation losses at the required oven temperatures. 

6. The time required for roasting a rolled rib roast of beef, rare, 
medium rare, and well done, was determined for various oven tem- 
peratures. The shortest time of roasting was at 160°C. (320°F.). (See 
Fig. 17.) 

7. The per cent loss of weight of the roasts was found to increase 
with the oven temperature used. (See Table V.) 

8. The energy required for roasting a rolled rib roast of beef in 
three types of electric ovens was determined for oven temperatures 
from 100° to 180°C. (212° to 356°F.). The most economical tem- 
perature for preparing rare and medium rare roasts was found to be 
100°C. in each oven. For well done roasts 120°C. (248°F.) is the 
most economical temperature. 

9. With electricity at 5 cents per kilowatt hour, it is at least 2 
cents cheaper to roast beef at 100° to 120°C. than at 180°C. 

10. It was found that at least 1000 watt-hours could be saved by 
searing the roast on top of the stove instead of heating the whole 
oven up to 250 °C, a saving of five cents on the basis of 5 cents per 
kilowatt hour for electric current. 



58 UNIVERSITY OF MISSOURI BULLETIN 

11. A method was devised for determining the most economical 
temperature for baking bread, cake, and biscuits. The minimum time 
of baking and the per cent loss of weight were determined for sev- 
eral oven temperatures. (See Table VIII.) 

12. The range of oven temperatures for baking biscuits was 
found to be from 200° to 240 °C. (392° to 464 C F.). Starting with the 
oven at the required temperature, the energy used in baking biscuits 
is practically the same for all oven temperatures. If it is necessary 
to heat up the oven from room temperature the most economical oven 
temperature is the lowest which will give satisfactory results; i. e. 
about 200°C. (392°F.). 

13. The range of temperatures for baking a small sized loaf of 
bread was found to lie between 180= and 240 °C. (356° and 464 : F.). 
Starting with the oven at the required temperature the most economi- 
cal temperature for baking bread is between 220° and 240 C C. When 
preheating is included, the most economical temperature for a small 
sized loaf was found to be between 200° and 215 C C. 

14. The range of temperature for baking sponge cake was found 
to lie between 170° and 190 C C. (338° and 374 C F.). ' For baking sponge 
cake the most economical oven temperature is the highest temperature 
which will give satisfactory results; i. e., about 190 : C. (374 : F. ). 

15. With electricity at 5 cents per kilowatt hour and allowing an 
interest and depreciation charge of 25 per cent, the most economical 
thickness of kieselguhr insulation was found for domestic use to lie 
between three and four inches. 

CONCLUSIONS 

Much has been accomplished recently by domestic scientists in sub- 
stituting accurate scientific methods of cooking for the vague and in- 
definite rules of our grandparents. There is. however, an enormous 
amount of work yet to be done before an inexperienced person can hope 
to get uniformly good results without first experiencing many failures 
and wasting much good material. 

With reference to the use of a thermometer for the standardization 
of oven temperatures Miss M. B. Van Arsdale, 1 assistant professor 
of household arts at Columbia University, says, "'Regarding the inex- 
perienced housewife it can truly be said that with an accurate ther- 
mometer her results would undoubtedly be more uniformly good — and 
we believe that the recipe books of the future should not read merely 
'bake until done in a moderate oven' or 'according to judgment.' but 
will also state how long and at what temperature, so that in the hands 
of even the inexperienced these recipes will yield not occasionally good 



1. Technical Educ. Bui. No. 22. Columbia Univ. 



THE ECONOMICS OF ELECTRIC COOKING 59 

but uniformly good results without the discouragement of many fail- 
ures, the sacrifices of much time and the waste of much good material. 
Thus the scientific treatment of the subject added to our traditional 
knowledge should tend to evolve an even higher type of cookery than 
we have had in the past." 

The present lack of definite rules for cooking is due in a large 
degree to the absence of adequate means of controlling the temperature 
of the food. When using the ordinary wood or coal cooking range the 
degree of heat is controlled chiefly by dealing with the food itself 
rather than by regulating the heat at the point of combustion. The 
amount of draft necessary to promote the combustion of the fuel 
causes too great a degree of heat in the oven or on the stove to enable 
the cook to deal with the food in the proper way except by constantly 
watching it, stirring it, and changing the position of the vessel on the 
stove or in the oven. 

With the advent of electric ovens a revolution in the methods of 
cooking has become possible. Not only can the temperature of the 
electric oven be accurately controlled but the necessity of constant 
vigilance is removed. Apparatus can be designed for making the 
whole process practically automatic. Some kinds of food can even 
be prepared in advance, placed in the oven, and without any further 
attention on the part of the housewife the current will automatically 
be turned on at a predetermined time. The temperature of the oven 
will increase to the desired value and there remain constant until 
the food is properly cooked. 

With this method perfected the advantage of electric cooking over 
the other methods will be great and in most cases the cost will not 
be excessive. To the possibility of obtaining uniformly well-cooked 
food should be added the saving to the housewife in time and worry 
and the absence from the kitchen of excessive heat. 

The present day problem in electric cooking is to determine the 
methods of cooking that will yield the most in nutrition and flavor and 
to formulate definite rules or directions so that a particular article 
of food can be cooked in the best possible manner by persons of ordi- 
nary skill. The engineer's problem is then to design practical cook- 
ing devices in which the temperature can be accurately regulated with 
a minimum of attention on the part of the housewife. 

Electric cooking may be classified according to the temperature to 
be used in the oven. The baking of bread, cake, and pastry requires 
a high oven temperature. In the average family where the oven is 
used intermittently a large part of the electricity used in this class 
of baking will go to heat up the oven from room temperature to the 
required baking temperature. In other words the preheating loss 
will be large compared with the radiation and convection loss. 

The preparation of vegetables, cereals, and meats (except for 
searing, broiling, and frying) requires a low degree of heat, applied 



60 UNIVERSITY OF MISSOURI BULLETIN 

for several hours. In this class of cooking the preheating loss forms 
but a small part of the total loss, while the radiation and convection 
loss is a large part of the whole. 

It is evident that the characteristics of properly designed ovens 
differ for the two kinds of cooking. An oven to he used for baking 
at the high temperature should have the preheating loss reduced to 
a minimum. A large-sized heating element should be used for the 
preheating and be automatically cut off as soon as the oven reaches 
the desired temperature. A smaller coil will then suffice to keep the 
oven at the required temperature by supplying enough heat to balance 
the losses and the heat absorbed by the food. Unless it is planned to 
frequently use the oven for several hours at the same temperature as 
in baking several batches of bread or cake, it will not pay to increase 
the heat insulation of the oven to such an extent as where the pre- 
heating loss is smaller. Since in cooking at the lower temperatures. 
the preheating loss is small compared with the radiation and convec- 
tion loss, the latter then becomes the more important and a thicker 
heat insulation can be economically used. 

For baking at the higher temperatures a heating element in the 
upper part of the oven is necessary to get the best results. Without 
the upper heating coil the bread, cake or biscuits will burn on the 
bottom before they are satisfactorily browned on top. For the lower 
temperatures this upper coil is unnecessary. 

Furthermore, for baking at the higher temperatures, the food 
and the heating coil must be separated several inches with a baffle 
between to secure more uniform heating and to prevent burning on the 
bottom. This arrangement, tho necessary, results in poor heat conduc- 
tivity between the heating element and the food. Hence, more energy 
will be required as indicated in the tests in heating water in the oven 
and on top of the stove. Since in cooking at the boiling point or below 
the food can be partly immersed in water, there is not the danger 
of burning as in baking. The baffle over the heating coil can, conse- 
quently, be dispensed with and the vessel of food can be placed directly 
on the heating element. A much better heat conductivity between the 
food and the heating element will result. Less energy will be re- 
quired for the first part of the cooking process when the food is being 
heated from the room temperature to the required cooking tempera- 
ture. 

As the size of an electric oven greatly affects the amount of the 
losses, an oven should be made as small as is practical for the size 
of the family that is to use it. For instance, oven Xo. 1 is uneconomical 
for a small family as several loaves of bread, cakes or tins of biscuits 
can be baked in it for the cost of one. For cooking at the lower 
temperatures the oven can be made smaller than for baking at the 
high temperatures as there is not the danger of the food burning due 
to non-uniform heating. For this class of cooking the utensils can 



THE ECONOMICS OF ELECTRIC COOKING 61 

fit snugly into the oven so that the size of the oven can be reduced 
to a minimum. 

The increased popularity of the fireless cooker indicates that 
people are learning that food can be cooked at temperatures lower 
than the boiling point of water. The particular temperature of 100 °C. 
(212 °F.) has long been the one used for cooking cereals, vegetables, 
and meats. This is because it is the easiest temperature to maintain 
at a constant value and not because it necessarily gives the best possible 
results. The fact that several hours are required for the cooking 
at lower temperatures is not a disadvantage when the process is 
automatic and does not require the attention of the housewife. Aside 
from the question of the quality of the food and the saving in electricity, 
four hours would probably be the most convenient time to allow for 
cooking food. The housewife could put in the food for the midday meal 
immediately after breakfast while the oven was still hot. "When it 
was taken out she could put in the evening meal so that the oven 
would be used continuously. The preheating loss would thus be reduced 
to a minimum. During the latter part of the afternoon the housewife 
would not need to be tied to her kitchen, since all that would be 
necessary at this time would be to dish up the food and serve it. 

The electric light and power companies should be interested in 
perfecting this method of cooking and in bringing it to the attention 
of their customers. A combination of the electric oven and the popular 
fireless cooker would be a very desirable load for the central station. 
It would be a steady all day load and would not interfere with the 
peak load even in the winter; as enough heat can be stored in a well- 
insulated oven to keep the food sufficiently hot for an hour or more after 
the current is turned off. 

The results of the cooking experiments in electric ovens indicate 
that it is possible to reduce the art of cooking to an exact science. 
If definite rules of time and temperature were formulated for cook- 
ing each article of food, the inexperienced housewife could obtain 
uniformly good results with the expenditure of a minimum amount 
of attention and fuel. 

The requirements for an electric oven for baking at the higher 
temperatures are, — minimum heat capacity of the oven, a large heating 
unit to heat up the oven from room temperature, an automatic device 
to cut out this heating unit as soon as the oven reaches the desired 
temperature, smaller heating coils to maintain the temperature at the 
desired value, a heating unit in the upper part of the oven, a baffle 
above the lower coils to distribute the heat, as small an oven as is 
practical for the size of family using it, and from two to four inches 
of heat insulation. 

The requirements of an electric oven for cooking at the lower 
temperatures are, — from three to four inches of heat insulation, a simple 
device for automatically controlling the temperature, a large coil for 



62 UNIVERSITY OF MISSOURI BULLETIN 

heating up the food from room temperature, placing the vessels of 
food directly on the heating units whenever possible, and a size of 
oven only large enough to contain the utensils to he used. 

The author begs to acknowledge his indebtedness to the Misses 
Stanley, Daniels, and Troxell of the home economics department of 
the University of Missouri for their many valuable suggestions and 
for their supervision of the bread, cake, and biscuit experiments; and 
to Messrs. Atkins, Brinkmeier, Crider and Macon for their assistance 
in taking readings during the progress of the work. 



THE 

UNIVERSITY OF MISSOURI 

BULLETIN 

ENGINEERING EXPERIMENT STATION SERIES 

EDITED BY 

E. J. McCAUSTLAND 

Dean of the Faculty of Engineering, Director of the Engineering 

Experiment Station 



Some Experiments in the Storage of Coal, by E. A. Fessenden and J. R. 
Wharton. (Published in 1908, previous to the establishment of the 
Experiment Station.) 

Vol. 1, No. 1 — Acetylene for Lighting Country Homes, by J. D. Bowles, 
March, 1910. 

Vol. 1, No. 2 — Water Supply for Country Homes, by K. A. McVey, 
June, 1910. 

Vol. 1, No. 3 — Sanitation and Sewage Disposal for Country Homes, by 
W. C. Davidson, September, 1910.. 

Vol. 2, No. 1 — Heating Value and Proximate Analyses of Missouri 
Coals, by C. W. Marx and Paul Schweitzer. (Reprint of report 
published previous to establishment of Experiment Station.) 
March, 1911. 

Vol. 2, No. 2 — Friction and Lubrication Testing Apparatus, by Alan E. 
Flowers, June, 1911. 

Vol. 2, No. 3 — An Investigation of the Road Making Properties of Mis- 
souri Stone and Gravel, by W. S. Williams and R. Warren Roberts. 

Vol. 3, No. 1 — The Use of Metal Conductors to Protect Buildings from 
Lightning, by E. W. Kellogg. 

Vol. 3, No. 2 — Firing Tests of Missouri Coal, by H. N. Sharp. 

Vol. 3, No. 3 — A Report of Steam Boiler Trials under Operating Condi- 
tions, by A. L. Westcott. 

Vol. 4, No. 1 — Economics of Rural Distribution of Electric Power, by 
L. E. Hildebrand. 

Vol. 4, No. 2 — Comparative Tests of Cylinder Oils, by M. P. Weinbach. 

Vol. 4, No. 3 — Artesian Waters in Missouri, by A. W. McCoy. 

Vol. 4, No. 4 — Friction Tests cf Lubricating Oils and Greases, by A. L. 
Westcott. 

No. 14 — Effects of Heat on Missouri Granites, by W. A. Tarr, and L. 
M. Neuman. 

No. 15 — A Preliminary Study Relating to the Water Resources of Mis- 
souri, by T. J. Rodhouse. 



The University of Missouri Bulletin — issued 

three times monthly; entered as second class 

matter at the postoffice at Columbia, Missouri. 

5000 




014 486 524 8 



